Method and apparatus for separating droplets for particles from a gas stream

ABSTRACT

A device for separating particles contained in a gas stream and the associated process use a spongy type separator to process gas streams containing liquid or solid particles of a size substantially smaller than one micrometer. The separator is advantageously made of a reticulated foam pierced with channels for the flow of the gas streams.

FIELD OF THE INVENTION

The present invention relates to the field of separators and morespecifically to means intended to separate droplets or particles from agaseous flow, whose size is less than or of the order of one micrometer.

BACKGROUND OF THE INVENTION

Many methods and devices have already been disclosed to that end.

U.S. Pat. No. 5,626,651 describes a process and a system of that typeaccording to which the turbulent gas stream flows above a series ofplates defining non turbulent zones where the particles are collected.More precisely, the plates are parallel to each other and vertical. Afiltering means made of fibers can also be provided between said platesin order to improve filtration notably of the finer particles.

International patent application WO-95/28,217 describes a device basedon the same principle, but according to which the plates are providedwith slots or replaced by grates. Frames covered with wire meshcontaining a fibrous mat are also used in this prior art.

Furthermore, patent application WO-97/00,102 relates to a separatorplaced at the exhaust of diesel engines in order to collect theparticles contained in the exhaust gas. A honeycomb structure piercedwith channels perpendicular to the opening of the honeycomb cells ispreferably provided. The porosity of such a structure is of the order of70%. However, this device cannot be used for fogs because the dropletstrapped in the cells cannot be removed by drainage.

International patent application PCT/FR-97/00,164 relating to aseparator with one or more vertical drains laterally delimited byfibrous corrugated elements is also known. An agglomerator is alsonecessarily placed upstream from the separator in order to have largerparticles that can be separated at the level of the separator. This istherefore relatively expensive and implies quite significant pressuredrops.

However, these well-known means do not allow effective collection andremoval of particles and/or droplets smaller than about one micrometer.In U.S. Pat. No. 5,626,651, the particles captured accumulate on thewalls, then fall onto the bottom of the device under the effect ofgravity. Means intended to shake the walls are often necessary to causethe particles accumulated on the walls to fall. This device posesproblems when very fine particles smaller than one micrometer are to beseparated. In fact, in this case, the height of the drain must be verylimited and the plates must therefore be very high so that the equipmentis very bulky for a very small section of flow. The same problem existsin the device according to document WO-95/128,217.

In patent application WO-97/00,102, the particles collected areoxidized.

SUMMARY OF THE INVENTION

The present invention proposes to solve the particle and/or dropletremoval problem in an original and unexpected way as explainedhereafter.

The present invention advantageously prevents any pressure drop due tothe fouling of a zone of the device; the pressure drop remains constantthroughout the life of the separator according to the invention.

Furthermore, the present invention allows to obtain a very highseparation rate by means of a small equipment with a low pressure lossand continuous running.

The present invention thus relates to a spongy type separator intendedto process gas streams containing liquid or solid particlessubstantially smaller than one micrometer or of the order of onemicrometer.

According to the invention, the separator is made of a reticulated foampierced with channels intended for turbulent flow of the gas streams,said channels being such that the gas streams flow through said foamfrom one end of the channels to the other.

The porosity of said foam specifically ranges between 90% and 98%,preferably around 97%.

Besides, the size of the cells forming said foam ranges between about0.5 mm and about 5 mm.

In particular, the diameter of the threads forming said foam rangesbetween 50 μm and 1000 μm.

According to the invention, the diameter of the channels running throughsaid foam ranges between 3 and 100 mm.

According to an aspect of the invention, said foam is made ofreticulated polyurethane.

According to another embodiment of the invention, said reticulated foamis made of a vitreous carbon; said foam can also be made from a metalsuch as aluminium, nickel or lead.

The device can further comprise a means for shaking said foam so as tocause the particles retained in the foam to fall.

According to a preferred use of the invention, the separator can be usedto remove liquid droplets such as the oil droplets initially containedin fogs. Said foam then provides regular drainage of the captureddroplets.

According to another embodiment of the invention, the device can be usedto separate solid particles suspended in a gas.

In other words, the present invention relates to a device intended toseparate particles contained in a gas stream, comprising a casing withan inlet and an outlet, at least one straight passageway, totally free,unsealed, open at both ends, intended to allow passage of said gasstream in turbulent state from the inlet to the outlet, a reticulatedfoam material which defines the walls of said passageways and fills allthe space between said passageways, said foam material being made up ofthreads forming interconnected pores or cells which communicate freelywith said passageways so as to create non-turbulent stagnant zonesextending away from said passageways.

According to the invention, said particles are collected and depositedon the surfaces of threads forming the reticulated foam material, saidthreads being spaced apart so that the cells defined thereby allowpassage of the turbulent stream over a distance of some cells (from saidpassageways) and prevent a direct gaseous flow from the inlet to theoutlet, the cells forcing the turbulences to decrease in thenon-turbulent zones occupying substantially all of the space between thepassageways.

According to a characteristic, said passageways all have the samedimensions.

More specifically, the length of the passageways ranges between about 10cm and about 200 cm.

The adjacent threads are advantageously spaced apart by a distance ofabout 0.5 mm to about 5 mm in each direction of the space, theperipheral threads and the spaces between said threads defining thewalls of said passageways. The particles are deposited on the threadsurfaces by inertial impact and by Brownian scattering phenomena.

Furthermore, the diameter of said threads ranges between about 50 μm andabout 1000 μm, and the reticulated foam has a porosity ranging betweenabout 90% and about 98%, preferably about 97%.

Besides, said reticulated foam is made of a polyurethane or PVC-coatedpolyurethane.

According to another possibility, said reticulated foam is made of avitreous carbon.

According to the invention, said reticulated foam is made of a metalsuch as aluminium, nickel or lead.

According to another embodiment of the invention, said reticulated foamis made of a ceramic material.

According to yet another embodiment of the invention, said passagewaysare made by assembly of reticulated foam sheets which form channels ofsquare or rectangular section.

In particular, said passageways are positioned horizontally, and thedevice allows to remove liquid droplets such as the droplets containedin an oil or water fog, the liquid formed after deposition of thedroplets being drained by said foam and continuously discharged from thecasing into suitable means placed at the bottom of said casing.

The passageways provided for the gas stream can be positionedhorizontally or vertically, and the particles are separated from the gasstream.

The invention also relates to a process for separating particles from agas stream in which they are contained, comprising the following stages:

passing said gas streams through at least one straight passageway,totally free, unsealed, open at both ends, in a given direction in acasing, above an area where the effluent is non-turbulent and stagnant,consisting of a plurality of interconnected subareas where there is nodirect flow and which communicates with the gas stream, and

arranging a plurality of surfaces transversely to the direction of flowof the gas stream, said surfaces extending from the passageways andbeing spaced apart so as to define said interconnected subareas formingthe non-turbulent area communicating freely with said passageways, eachsubarea occupying substantially all of the space between said adjacentsurfaces so that the turbulent eddies of gas stream enter said spacesbetween the surfaces and decay in said subareas, said particles beingtrapped and deposited mechanically on the surfaces defining the stagnantand turbulent-free subareas.

In a more detailed way, said stagnant and turbulent-free subareasconsist of the cells formed by adjacent threads of a reticulated foamwhich surrounds said passageways, the particles are carried along by theturbulent eddies within said gas stream in the cells between the threadsand are deposited on the thread surfaces by inertial impact and byBrownian diffusion mechanisms.

The invention is essentially aimed at particles with a diameter rangingbetween about 0.01 μm and about 100 μm, and the gas stream has avelocity in he passageways ranging between about 3 and about 20 m/s.

According to a particular feature of the invention, said passageways aremade by perforation or by drilling holes through sheets or blocks of amaterial made from reticulated foam.

Furthermore, said casing is periodically shaken or vibrated so as tocause the dust deposited on said threads of the foam to fall intosuitable means placed below the reticulated foam.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and improvements according to the inventionwill be clear from reading the description hereafter, given by way ofnon limitative example, with reference to the accompanying drawingswherein:

FIG. 1 is a perspective of a part of the separator according to theinvention,

FIG. 2 is a diagrammatical lengthwise section of an embodiment of theinvention, and

FIG. 3 is a simplified perspective of another embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a block made of a spongy material 1 according to theinvention. The material can advantageously be a reticulated polyurethanefoam or a reticulated PVC-coated polyurethane foam, a reticulatedvitreous carbon foam or a reticulated foam made from a metal such asaluminium, nickel or lead. A reticulated foam of a ceramic material canalso be used without departing from the scope of the invention.

The materials aimed at by the invention consist of small cells,dodecahedral for example, formed by intertwined threads, filaments orfine ligaments. The porosity usually ranges between 90 and 98%. The sizeof the cells ranges between about 0.5 mm and about 5 mm and the diameterof the threads ranges between 50 μm and 1000 μm. A thread diameterranging between 50 and 100 μm can sometimes be preferred.

Furthermore, channels 2, preferably parallel to each other, are piercedor drilled through spongy material 1. These channels allow the fluid toflow in the direction shown by arrows A in FIG. 1. The diameter ofchannels 2 ranges here between 3 and 100 mm. The distance between twochannels can range between about 2 mm and about 20 mm.

The cross-section occupied by drain channels 2 is 30 to 70% of the totalcross-section of said foam.

The section of the channels is preferably circular as shown in FIG. 1.However, the sections of the channels can have other shapes withoutdeparting from the scope of the invention.

The general layout of the channels can be such as to form a grid patternof parallel channels. However, a network of channels arrangeddifferently can be selected without departing from the scope of theinvention.

By way of example, a test has been carried out on the basis of areticulated polyurethane foam block pierced with 63 channels with each adiameter of about 6 mm and a length of 18 cm. The distance between thechannel centers is 12 mm. The rate of collection of particles of about1.5 μm in diameter is then 95%. The flow rate of the effluents is about30 m³/h and the pressure drop in the device is of the order of 0.75 kPa.This pressure drop can be even lower by increasing the to length of thechannels and their diameter by the same factor while keeping the samerate of collection.

Another example relative to the invention relates to the separation of awater fog with particles of about 30 μm in diameter in an air stream. Areticulated polyurethane foam with a cell size of about 0.5 mm is used.This foam is pierced with 162 circular horizontal 34-cm long channelswith a diameter of about 1 cm (distance between centers 1 cm). Thevelocity of the air in the channels is about 7 m/s with a pressure dropof about 0.3 kPa. A rate of collection of about 99.98% has thus beenobtained.

In the field of separation of droplets forming a fog, the presentinvention has the advantage of draining the droplets which thus form aliquid that flows by gravity through the reticulated spongy material.

An application example is illustrated by FIG. 2 which relates to aviscous fog separator in lengthwise section.

A mixture of gas and of oily fog flows in the direction shown by arrow Bin FIG. 2 into an enclosure 10 containing the spongy material.

The mixture flows through all the channels 2 pierced through the spongymaterial and leaves enclosure 10 in the direction shown by arrow C atthe other end of channels 2. The drainage obtained according to theinvention allows the oil to be collected at the bottom of enclosure 10.This oil can itself be discharged and stored in a tank or in any otherspecific means such as 3. The oil captured by the threads forming thespongy material thus flows to the bottom of the device substantially atthe same flow rate as when it is absorbed.

In other words, the spongy material is saturated with liquid over alimited height, corresponding to the rate of absorption of the threadsof the spongy material, limited by the allowed discharge rate.

Separation of an oily fog with particles having a diameter of about 1 μmhas been performed in an air stream a reticulated polyurethane foamwhose cell size is about 0.5 mm is used. This foam is pierced with 162horizontal 68-cm long channels with a diameter of about 1 cm (distancebetween centres 1 cm). The velocity of the air in the channels is about10 m/s. A pressure drop of the order of 1.8 kPa is measured and a rateof collection of 96% is obtained.

In relation to separators made up of fibrous mats or others, the presentinvention allows to do without a frame or any other element intended tosupport the mat since the spongy material according to the invention isinitially rigid enough to be perforated by any means known in the art.Furthermore, a high drilling precision can be obtained.

The device according to the invention is suited for separation of gasstream fumes. Deposition then occurs on the threads of the reticulatedfoam where a solid or bituminous layer forms.

The particles being present in low concentrations, cleaning and/orchanging of the foam is very little frequent.

Furthermore, without departing from the scope of the invention, thereticulated foam according to the invention can be washed when it isdirty and put back in place when clean.

The device according to the invention is also suited for separation ofindustrial dust. In this case, the channels are preferably positionedvertically so that the dust deposited on the threads can be removedtherefrom by vibrating the device. The dust thus falls by gravity intothe channels in which flow is stopped during cleaning.

Another example relating to the fumes coming from a FCC catalyst isgiven: the particles are about 6 μm in diameter. The foam is made ofreticulated ceramic with cells of about 2 mm. 88 circular channels,either horizontal or vertical, with a diameter of about 1.3 cm, runthrough said foam from one end to the other. The distance betweencentres of the channels is about 1.3 cm. Three foam portions of about 23cm each are arranged in series (total length of about 70 cm). Thevelocity of the air in the channels is about 7 m/s and a pressure dropof about 0.25 kPa has been measured. A rate of collection of about 94%has thus been obtained according to this example.

Without departing from the scope of the invention, a device such as thatdiagrammatically shown in FIG. 3 can be used.

The separator consists here of an assembly of sheets or plates 4 ofreticulated foam forming a grid pattern through which the effluents tobe processed flow. The plates are contained in a casing 5.

As in the previous embodiments of the invention, the effluents to beprocessed flow in as shown by arrow B, flow through channels 2 from oneend to the other and flow out as shown by arrow C.

According to an application example, the sides of the squares of thegrid pattern are 1.25 cm long. The foam plates are about 3 mm thick. Thefoam is a nickel foam with 30 and 40 cells (or pores) per inch. The sizeof the cells is of the order of 0.75 mm with threads of about 50 μm indiameter.

The grid pattern can also consist of rectangles or of other geometricshapes obtained from intertwined reticulated foam plates 4.

According to this example, the channels are 18 cm long. The separator is11.5 cm high and 49.5 cm long (front view). FIG. 3 globally illustratesthis geometry.

What is claimed is:
 1. A separator intended for processing of gasstreams containing liquid or solid particles substantially smaller thanone micrometer or of the order of the one micrometer, comprisingreticulated foam delimiting channels intended for turbulent flow of thegas streams, said channels being such that the gas streams flow throughsaid foam from one end of the channels to the other, wherein said foamincludes cells adjacent said channels forming stagnant andturbulent-free subareas into which said liquid or solid particlescarried by eddies of the gas streams are deposited.
 2. A separator asclaimed in claim 1, characterized in that the porosity of said foamranges between 90% and 98%.
 3. A separator as claimed in claim 1,characterized in that a size of the cells ranges between about 0.5 mmand about 5 mm.
 4. A separator as claimed in claim 1, characterized inthat said foam comprises threads having diameters ranging between 50 μmand 1000 μm.
 5. A separator as claimed in claim 1, characterized in thatsaid channels running through said foam have a diameter which rangesbetween 3 and 100 mm.
 6. A separator as claimed in claim 1,characterized in that said foam comprises a reticulated polyurethane. 7.A separator as claimed in claim 1, characterized in that saidreticulated foam comprises a vitreous carbon.
 8. A separator as claimedin any one of claim 1, characterized in that said reticulated foamcomprises a metal.
 9. A separator as claimed in claim 1, furthercomprising means for shaking said foam in order to cause the particlesdeposited in said foam to fall.
 10. A separator as claimed in claim 2,characterized in that the porosity of said foam is around 97%.
 11. Aseparator as claimed in claim 8, characterized in that said reticulatedfoam comprises a metal selected from the group consisting of aluminum,nickel and lead.
 12. A device intended for separation of particlescontained in a gas stream, comprising a casing with a n inlet and anoutlet, at least one straight passageway totally free, unsealed, open atboth ends and intended to allow passage of said gas stream in turbulentstate from the inlet to the outlet, a foam material which defines thewalls of said at least one straight passageway, said foam materialcomprising threads forming interconnected pores or cells thatcommunicate freely with said at least one straight passageway so as tocreate non-turbulent stagnant zones which extend away from said at leastone straight passageway, characterized in that said particles arecollected and deposited on the surface of the threads forming the foammaterial, said threads being spaced apart so that the cells definedthereby allow passage of the turbulent stream over a distance of somecells from said at least one straight passageway, but prevent a directgaseous flow from the inlet to the outlet, the cells forcing turbulences to decrease in the non-turbulent zones.
 13. A device as claimed inclaim 10, characterized in that a plurality of straight passageways areprovided and in that said foam material fills all of the space betweenpassageways.
 14. A device as claimed in claim 10, characterized in thatsaid foam material is a reticulated foam material.
 15. A device asclaimed in claim 13, characterized in that said passageways all have thesame dimensions.
 16. A device as claimed in claim 13, characterized inthat a length of said passageways ranges between about 10 cm and about200 cm.
 17. A device as claimed in claim 12, characterized in that t headjacent threads are spaced apart by a distance of about 0.5 mm to about5 mm in each direction of the space, peripheral threads and the spacesbetween said peripheral threads defining the walls of said at least onestraight passageway, and in that the particles are deposited on thesurfaces of the threads by inertial impact and by Brownian scatteringphenomena.
 18. A device as claimed in claim 14, characterized in thatthe diameter of said threads ranges between about 50 μm and about 1000μm, and a porosity of the reticulated foam ranges between about 90 and98%.
 19. A device as claimed in claim 14, characterized in that saidreticulated foam comprises of a polyurethane or a PVC-coatedpolyurethane.
 20. A device as claimed in claim 18, characterized in thatsaid reticulated foam comprises a vitreous carbon.
 21. A device asclaimed in claim 14, characterized in that said reticulated foamcomprises a metal.
 22. A device as claimed in claim 14, characterized inthat said reticulated foam comprises a ceramic material.
 23. A device asclaimed in claim 13, characterized in that said passageways are made byassembly of reticulated foam sheets forming channels of square orrectangular section.
 24. A device as claimed in claim 13, characterizedin that said passageways are positioned horizontally, whereby liquiddroplets can be removed from the gas stream, liquid formed afterdeposition of the droplets being drained by said foam and continuouslydischarged from said casing into a tank placed at the bottom of saidcasing.
 25. A device as claimed in claim 14, characterized in that saidpassageways are positioned vertically.
 26. A device as claimed in claim18, characterized in that the porosity of said foam is around 97%.
 27. Adevice as claimed in claim 21, characterized in that said reticulatedfoam comprises a metal selected from the group consisting of aluminum,nickel and lead.
 28. A process for separating particles from a gasstream in which they are contained, comprising the following stages:passing said gas streams through at least one straight passageway, andarranging a plurality of surfaces transversely to the direction of flowof the gas stream, said surfaces extending from said at least onestraight passageway and being spaced apart so as to define a pluralityof interconnected subareas forming together a stagnant and non-turbulentarea communicating freely with said at least one straight passageway,each subarea occupying substantially all of the space between adjacentsurfaces so that turbulent streams of the gas stream enter said spacesbetween the surfaces and decay in said subareas, said particles beingtrapped and deposited mechanically on the surfaces defining the stagnantand non-turbulent area.
 29. A process as claimed in claim 28,characterized in that said stagnant and non-turbulent area comprisecells formed by adjacent threads of a reticulated foam which surroundssaid at least one straight passageway, the particles being carried alongby turbulent eddies within said gas stream in the cells between thethreads and deposited on the thread surfaces by inertial impact and byBrownian diffusion mechanisms.
 30. A process as claimed in claim 28,characterized in that the diameter of said particles ranges betweenabout 0.01 μm and about 100 μm, and the velocity of the gas streamranges between about 3 and about 20 m/s in said at least one straightpassageway.
 31. A process as claimed in claim 28, characterized in thatsaid at least one straight passageway is mad e by perforation or bydrilling at least one hole through sheets or blocks of a reticulatedfoam material.
 32. A process as claimed in claim 28, characterized inthat said casing is periodically shaken or vibrated so as to cause theparticles deposited on said threads to fall from the foam into a tankplaced below the reticulated foam.